The present invention relates generally to a position sensing apparatus. It finds particular application to laboratory fume hoods having one or more moveable doors in which the rate of exhaust is varied in accordance with the extent to which the doors are open. Although the present invention is described herein primarily in reference to laboratory fume hood doors, it will be appreciated that the present invention is also amenable to other structures which are generally moveable along a predetermined path.
Fume hoods are used in laboratories and other like environments to provide a work place where potentially dangerous chemicals are used. Such fume hoods generally comprise an enclosure having moveable doors at the front portion thereof which can be opened in various amounts to permit access to the interior of the enclosure. The enclosure is typically connected to an exhaust system for removing any noxious fumes so as to avoid exposure to persons working in or near the hood.
Conventionally, fume hood controllers control the flow of air through the fume hood to maintain desired flow characteristics to efficiently exhaust the fumes from the enclosure. Typically, the air flow is a function of the desired average face velocity of the opening of the fume hood. The average face velocity is the flow of air into the fume hood per square foot of open face area of the fume hood.
The sash doors of some fume hoods can be opened by raising them vertically. Other hoods have a number of doors that are mounted for horizontal sliding movement, typically in two or more sets of tracks. Fume hoods in which horizontally sliding doors are mounted in a vertically movable frame for two modes of opening are also known. Prior fume hood controllers have included sensing means for measuring the absolute position of vertical doors and/or the relative positions of horizontal doors and then using a signal proportional to the sensed position to vary the speed of the blowers or to vary the position of the dampers. A drawback of sensing relative sash position is the use of very large indicators, for example, elongated magnets traversing the entire width of each sash.
Position sensors using a magnet indicator and an array of sensor elements, such as Hall effect sensors, are generally known in the art. Because Hall effect sensors have high power consumption, a multiplexing scheme is often used in which the sensors are individually enabled and their output scanned sequentially. See, for example, U.S. Pat. No. 5,589,769 to Krahn, which discloses a position sensor including an array of transducers (22) wired to a multiplexer (30). Similarly, U.S. Pat. No. 5,534,849 to McDonald et al. discloses a position sensor which uses multiple magnetic field sensors (12) mounted on a door frame and magnet actuators (15A, 15B, 15C) mounted on a movable door. The magnetic field sensors are preferably Hall effect semiconductor devices. The sensors are enabled and sampled one at a time using multiplexer (18). U.S. Pat. No. 5,733,188 to Jacob discloses a multiplexer (130) in a fume hood sash position sensing system.
Accordingly, the present invention contemplates a new and improved position sensing apparatus and fume controller which overcomes the above-referenced problems and others.
In a first aspect, a method is provided for determining the position of one or more sashes in a frame is provided, wherein the frame defines an opening and the sashes are movable to change an extent to which the sashes cover the opening. The frame is divided into a plurality of distinct regions along its length and a sensor element is associated with each region to form a sensor array. The sensor elements are responsive to indicator elements carried on each sash when aligned therewith. The position information is determined by capturing sensor state information for each sensor in the array in parallel.
In a second aspect, the present invention provides a sash position sensing system for a fume hood having a plurality of movable sashes in a frame includes an indicator element affixed to each sash and an array of sensor elements extending along the frame in the direction of sash motion. The sensor elements interact with said indicator elements when generally aligned. A computer-based information handling system is coupled to the array of sensor elements, which recording state information for each sensor element simultaneously.
In a third aspect of the subject invention, a fume hood includes a housing having an opening formed therein and a plurality of sashes movable to cover and uncover portions of the opening. An indicator element is affixed to each sash and an array of sensor elements extend along the frame. The sensor elements interact with the indicator elements when aligned. A computer-based information handling system, which is coupled to the array of sensor elements, records state information for each sensor element simultaneously.
One advantage of the present invention is that absolute sash position is calculated.
Another advantage resides in the use of low power consumptive sensors.
Another advantage of the present invention is that a multiplexed sensor array is not required, thus eliminating the need for intermittent sensor operation.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.